1. Field of the Invention
The present invention relates to an underwater cutting and pelletizing apparatus that produces resin pellets.
2. Description of the Related Art
An underwater cutting and pelletizing apparatus has a cutting device, a separation device installed at a position higher than the cutting device, and a tank installed below this separation device. Between this cutting device, separation device and tank are connected for water supply, thereby forming a circulation path of water in the overall underwater cutting and pelletizing apparatus (for example, refer to Japanese Patent Application Publication No. 2006-110777).
The cutting device makes pellets by finely cutting molten resin, which is pressurized and supplied by a resin kneader, in a water chamber. These pellets are discharged from the water chamber along with water, and fed to the separation device. The separation device is for separating water from the pellets sent out from the water chamber of the cutting device with water. In addition, the tank stores the water discharged from the separation device for a short term. The water leaving the tank is cooled to a predetermined temperature, and then supplied to the water chamber of the cutting device again.
It should be noted that the water sent from the cutting device to the separation device is called carrier water due to having a function of carrying the pellets; however, hereinafter the water circulating in the entirety of the underwater cutting and pelletizing apparatus (i.e. including water returned from the separation device to the tank and cutting device) is all called carrier water.
The reason that the installation position of the separation device is higher than the cutting device as described above is to prevent (impart backpressure) cavitations from occurring in the water chamber of the cutting device, to cool the water as much as possible by lengthening the carried distance of the carrier water to a certain extent, and the like.
As a result, the separation device is installed at a location that is higher than the cutting device such as on a higher floor of the building in which the cutting device is installed, a result of which the height difference between the separation device and the tank is also large. For example, with a large-scale underwater cutting and pelletizing apparatus such as that in which the volume of water ejected from the water chamber of the cutting device toward the separation device exceeds 600 m3/h, the height difference from the separation device to the tank may reach 20 to 30 m.
Conventionally, no energy is recovered from the carrier water sent from the separation device to the tank, and thus the potential energy has been wasted.
On the other hand, the inside of the water chamber of the cutting device is controlled to be constant at approximately 50° C. to 80° C. so as to be suitable for the cutting of molten resin. Therefore, the water temperature of the carrier water ejected from the water chamber of the cutting device (towards the separation device) is 90° C. or more.
As a result, a cooling device (heat exchanger) is installed in the midstream of the path supplying this carrier water to the water chamber of the cutting device again through the tank, whereby the temperature of the carrier water is cooled to approximately 50° C.
The amount of heat that is radiated by this heat exchanger, i.e. the amount of heat absorbed by the carrier water from the molten resin in the water chamber of the cutting device, is not used in any way, and the thermal energy has thus been wasted.